Water purification apparatus and units for use in laboratories and healthcare facilities are well known. Generally, they involve the reduction and/or removal of contaminants and impurities to very low levels. They typically contain a variety of technologies that remove particles, colloids, bacteria, ionic species and organic substances and/or molecules.
Many analytical laboratories now require a purified stream of ‘ultra-pure’ or ‘ultra-purified’ water, which can be considered as purified water having a resistivity of >10MΩ·cm (herein all at 25° C.), preferably >15MΩ·cm or higher. This is of particular importance where such laboratories are involved in research requiring the highest possible purity. Advanced analytical techniques or processes requiring the highest possible purity of water include ion chromatography, high performance liquid chromatography, ICP/mass spectroscopy, etc. Analysers in laboratories, typically medical laboratories, are often automated to carry out a sequence of analyses on samples such as blood or urine. Again these analysers require an immediately available quantity of highly purified feedwater, typically ultra-pure water.
Typically in such analytical techniques or processes, only relatively small volumes of such ultra-pure water are required. Meanwhile, greater volumes of water are required for more general duties in the same location, generally in laboratories, such as rinsing of glassware and containers, and the preparation of bulk reagents from concentrated standards, etc. However, the water purity or quality for such purposes, whilst still needing some degree of purification compared with general water sources, need not be of the highest possible purity or of an ‘ultra-pure’ standard.
To provide both ultra-pure water and more general purified water, two separate water purification systems or supplies, each dedicated to providing the appropriate quality for the specific application, could be provided, but with attendant cost. Alternatively, a single water purification unit could be provided to provide all the purified water, but it must operate at the highest quality for the analytical techniques, making it expensive to operate for the larger volumes of more general purified water.
Another requirement of analytical techniques and processes is that although only low volumes are required, such low volumes must be available at all times irrespective of any other supply requirements from the water purification unit or system. However, all water quality deteriorates over time, generally through any period of being static or stationary such as in a reservoir, and this problem is greater or more acute the higher the water purity.
Analysers typically require water in a cyclical manner and at a relatively high flow-rate, but only for short periods, thus giving a known volume requirement and delivery schedule.